Study On Recovery And Purification Of Tellurium From Copper Anode Slime And Relative Fundamental Theory

Tellurium, which is called the vitamin of industry and the bridge of modern advanced technologies, plays more and more important role in material field. Much attention is paid on recovery of tellurium from tellurium-containing materials and preparation of high pure tellurium by a cheap and efficient method because its resource is scarce. Tellurium comes mainly from copper anode slime. It is very valuable to study on recovery and preparation of tellurium. A novel method is invented, which includes extraction and recovery of tellurium from copper anode slime by preleaching copper with H2SO4, deleading with Na2CO3, removing selenium by roasting de-lead anode slime mixed with concentrated sulfur acid, leaching tellurium and bismuth with HCl from roasted anode slime, reducing Te(IV) in leachate with SO2under the action of Cl-and purifying tellurium by chemical method. Reduction catalytic mechanism of halogens ion on Te(IV) in the H2SO4solution and thermodynamic analysis on removal of impurities during the purification are studied in this paper.Firstly, copper-containing solution is obtained after preleaching copper anode slime with H2SO4. Leaching rate of copper and tellurium are89.5%and20.4%when reaction temperature is80℃, molar ratio of H2SO4to Cu in the material is1.5:1, ratio of liquid to solid is3:1and reaction time is1.5h.Mixed with Na2CO3, de-copper anode slime is grinded for3h, PbSO4is transformed into PbCO3when molar ratio of Na2CO3to Pb in anode slime is2.5:1, ratio of liquid to solid is2:1, quality ratio of steel ball to anode slime is8:1. SO42-is removed by washing. Subsequently, lead is leached with HNO3. Leaching rate of lead is70%when molar ratio of HNO3to Pb in de-copper anode slime is6:1.Se is removed by roasting after de-lead anode slime is mixed with concentrated sulfuric acid. Removal rate of Se reaches95%when molar rate of H2SO4to sum of both Se and Te is1.2:1, reaction temperature is680℃and reaction time is3h. tellurium-containing leachate is obtained by leaching with HCl after removal of Se by vaporation. Total extracting rate of tellurium in copper anode slime is93.6%when concentration of HCl acid is6mol·L-1, rate of liquid to solid is3:1, reaction temperature is80℃and reaction time is2h. At the same time, some noble metals such as gold and sliver are enriched, contents of gold in anode slime increases from0.152%to0.34%, and sliver increases from7.81%to14.34%.Crystallization mother solution is acquired by evaporating and crystallizing pre-leachate under normal temperature. Se in solution is separated beforehand by reduction with SO2. Removal rate of Se in the2L solution is96.50%and precipitation rate of tellurium is less than1.05%when reaction temperature is80℃, concentration of sulfur acid is240g·L-1, flow of SO2is35ml·min-1and reaction time is2h. Recovery rate of tellurium reaches99.60%under the action of Cl-and SO2after removal of selenium.Crystallization mother solution, in which concentration of H2SO4is in the range of880g·L-1～1000g·L-1, is acquired after copper has been recovered from solution by deep evaporation. Tellurium in the crystallization mother solution is recovered under the action of Cl-and SO2, and its recovery rate reaches99.25%when reaction temperature is85℃, concentration of H2SO4is880g·L-1, concentration of Cl-is0.5mol·L-1, flow of SO2is40L·h-1and reaction time is2h. Result of5m3volume industrial experiment indicates that recovery rate of tellurium is98.32%, mass percents of Te, Cu and Cl in solid product are51.10%,27.35%and13.68%, respectively. XRD result shows that elemental tellurium and Cu2Cl2have existed in the product.Compared with thiourea complexation leaching and oxidation with H2O2-leaching with sulfur acid, leaching with HNO3is chosen as a way to separate copper from tellurium in the Cu-Te residue. Stoichiometric dosage of HNO3can be calculated according to rules that Cu2Cl2is transformed into CuCl2and Cu(NO3)2, Te is transformed TeO2and HNO3playing oxidation role is transformed into NO2. Removal rate of copper reachs97.5%and leaching rate of tellurium is1.05%when dosage of HNO3is0.96time of stoichiometric dosage, and tellurium is tranformed into TeO2.Powdered tellurium is obtained after Se has been removed beforehand and Te is treated twice by method of oxidation, leaching and reduction.Finally,4N+tellurium satisfied with standard of YS/T222-1996is acquired after powdered tellurium is treated under450℃and hydrogen ambient.Catalytic mechanism of Cl-on reduction of Te (Ⅳ) is studied by means of methods such as ion-exchange, UV-VS spectrophotometry, XRD and determination of solubility. The results show that Te(IV) exists in form of TeOOH+when concentration of H2SO4in solution is less than700g·L-1, TeOOH+is gradually dehydrated and changed Te2O3SO4when concentration of H2SO4is over700g·L-1. Therefore, Te (Ⅳ) becomes more stable and more difficult to be reduced by SO2. Structure of Te2O3SO4in high concentration H2SO4solution is destroyed by Cl-, with the increasing of Cl-concentration,Te(Ⅳ) is transformed step by step into TeOCl2, TeCl4and H2TeCl6, and Te(IV) is getting more and more active. The study on catalytic kinetic of Cl-shows activation energy is44.87kJ·mol-1when Cl-concentration is0.1mol·L-1, and activation energy is36.714kJ·mol-1when Cl-concentration is0.3mol·L-1. XRD results confirm that product is elemental tellurium when Cl-and Br-are used as catalyst, the product is Tel (Te4I4) when I-is used as catalyst.Distribute ratio of elements in the tellurium-containing residue during purification and thermodynamic analysis show that impurities can be removed efficiently and high pure tellurium can be obtained by oxidizing with HNO3and leaching with H2SO4, removing selenium beforehand, oxidizing-leaching-reducing and treating under hydrogen ambient and high temperature. Impurities such as Cu, Pb, Sb and Ag in powdered tellurium combine with Cl-to form complexes and are kept in the solution together with Ca, Al, Mg and Fe when concentration of HC1in solution is not less than6mol·L-1. Arsenic is evaporated in forms of As4O6, Se is removed in form of H2Se under450℃and hydrogen ambient.Compared with traditional technologies, this technology on extracting tellurium has many advantages such as large treatment capacity of convert, low consumption of energy and acid, little flue gas volume. Contrasted to the traditional method in which precipitating tellurium with copper powder, the catalytic reduction method has its advantages such as low cost, high content of tellurium in the product and easy treatment. High pure tellurium is prepared by chemical method. This method has advantages such as easy control, low cost, high direct recovery rate, stable quality of product and large scale.